Date: Thu, 19 Aug 2010 14:58:28 +0200
From: Andi Kleen <andi@firstfloor.org>
To: Matthew Wilcox <matthew@wil.cx>
Cc: Andi Kleen <andi@firstfloor.org>, Namhyung Kim <namhyung@gmail.com>,
        Arnd Bergmann <arnd@arndb.de>, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH] introduce ptr_diff()
Message-ID: <20100819125828.GA6729@basil.fritz.box>
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 <20100819124017.GI12892@parisc-linux.org>
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On Thu, Aug 19, 2010 at 06:40:17AM -0600, Matthew Wilcox wrote:
> On Thu, Aug 19, 2010 at 02:23:09PM +0200, Andi Kleen wrote:
> > IMHO it would be better to simply disable the warning in sparse instead
> > of uglying the code just to work around sparse bogosity. It doesnt' seem
> > to make much sense. A subtraction followed by a shift is not expensive.
> 
> What makes you think it's a shift?  struct page isn't necessarily a
> power of two in size.  The original poster said "allyesconfig" which is
> going to add in KMEMCHECK and WANT_PAGE_DEBUG_FLAGS.  I think that makes
> it 76 bytes on x86-32, so sparse is right to warn.

These can be still implemented cheaply. Small constants generally are
The only thing that would be really expensive is division by unknown number.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.
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